Electrolytic cell



Dec. 31, 1963 J. D. SCARBER ELECTROLYTIC cram.

Filed Oct. 4, 1960 IIIIIIIIIIIIIJ'IIII IIIWfI,

INVENTOR. JOSEPH D. SCARBER ATTORNEY United States Patent 3,116,227 ELEC'IRDLYTTC QELL Joseph D. Scarher, Port Arthur, Tern, assignor to Gulf Oil Corporation, Pittsburgh, Pa, a corporation of Pennsylvania Filed Oct. 4, was, Ser. No. 6 3,468 5 Claims. (til. Ella-258} This invention relates to an improved apparatus for conducting electrolysis reactions and more particularly to an improved apparatus for the electrolysis of aqueous salt solutions, for example, the electrolysis of aqueous sodium chloride to produce chlorine, hydrogen and sodium hydroxide.

Electrolytic alkali halogen cells are well known in the art and have been used widely in industry since about the turn of the century. These electrolytic cells are primarily of two types, i.e., the mercury type, and the foraminous diaphragm type. A foraminous diaphragm is a permeable barrier placed between the anode and the cathode. The pores of the foraminous diaphragm must be small enough to reduce back mixing of the fluids in the cathode chamber With the fluids in the anode chamber, but large enough to permit ions to pass therethrough by electrical migration. The commercial foraminous diaphragm cells are also of several types. They can be classified as rectangular or cylindrical, depending on the design of the electrodes, and they can be either of the unsubmerged or submerged cathode type. The terms unsubmerged and submerged do not indicate the depth of submersion, but rather whether there is liquid on one side (unsubmerged) or on both sides (submerged) of the cathode. The improved design of the electrolysis cell of the present invention is of the foraminous diaphragm type, and the design is such that the cell can be employed with the cathodes submerged or unsubmerged.

In all of the cells involving the electrolysis of aqueous salt solutions the object is to decompose the salts efficiently. The design of the cell should be such that intermingling of the products in the anode and cathode chambers is minimized and thus formation of side reactions and by-products, which attack and destroy the anodes, is appreciably curtailed. In addition, the aqueous salt solutions to be decomposed must be carefully purified to remove small amounts of impurities such as magnesium and calcium compounds therefrom, which impurities, if not removed, will tend to plug the foraminous diaphragm and thus impair electrical efiiciencies. Despite efforts to purify the aqueous salt solutions and to prevent intermingling of the cathodic and anodic products, some intermingling does inevitably occur, and some impurities manage to find their way into the system. It is always necessary, therefore, to replace parts of the cell, such as the diaphragm or the electrodes, at various intervals. Ease of replacement of these various components is, consequently, of importance in reducing down time and thereby increasing the yields of products per cell per unit of time. The improved cell of this invention is designed for ease of assembly and disassembly. There are no nuts and bolts required to hold the component parts of the cell together. Consequently, no tools are needed to assemble and disassemble the improved cell of this application. The electrical contacts in the cell can be maintained, for example, by spring tension, thus eliminating the need for bolts or the need for embedding the electrodes in metal. Gaskets can be employed in place of caulked seams throughout the cell. For example, a gasket can be employed as a seal between the cathode chamber and the anode chamber which surmounts it. In the improved design of the electrolysis cell of this application, each anode is supplied with its own individual cathode which completely surrounds said anode. Usually, a plu- "ice rality of these individualized anode-cathode units are employed in a cell so that any number of units can be put into or taken out of service with a minimum of disturbance to the operation. For example, if one of the individual anodes is corroded, it can be removed and the cathode plugged by any suitable means, such as with a plug of hard rubber, or other inert material, or in the alternative, the individual anode can be removed along with the individual cathode with provision made for plugging the opening between the anode and the cathode chambers.

Additional advantages are gained when cylindrical anodes surrounded by cylindrical cathodes are employed. One advantage is that the cylindrical cathode surface is equidistant from the cylindrical anode surface and thus the current between the cylindrical surfaces will be more uniform and the cathode and anode will erode more evenly. Another advantage is gained when cylindrical anodes and cathodes are employed, for readily available sheet asbestos material can be used for the foraminous diaphragm which is disposed between said anode and cathode. Usually, the foraminous diaphragm material is placed onto the cathodes in such a way that the foraminous diaphragm is contiguous with the surface of the cathodes. It is difficult to obtain for most cells a foraminous diaphragm which fits the contour of the cathode employed and remains contiguous with the surface of said cathode. This problem is eliminated when cylindrical cathodes are employed, for readily available sheet asbestos can be employed which easily fits the contour of the inner surface of the cathode cylinder when a rolled sheet of asbestos of the proper dimensions is placed inside each cathode cylinder and allowed to expand. The force or pressure exerted by the feed on the anodic side of the foraminous diaphragm is more than su'liicient to maintain the diaphragm contiguous with the inner surface of the cathode. In addition, by utilizing cylindrical anodes and cathodes, more eddy currents are produced in the cell which discourages the promotion of by-products which might attack and thus lessen the life of the electrodes.

Gther objects and advantages will become more apparent as reference is made to the accompanying drawings, wherein a preferred embodiment of the invention is illustrated and in which:

FIGURE 1 is a vertical view, partially in section, of the cell showing the electrodes and the positioning of the component parts in the cell;

FIGURE 2 is an enlarged view of one individual anodecathode assembly, partially in section, revealing the spring design utilized to make the electrical connections for the electrodes; and

FIGURE 3 is a top view of the cell along the section line shown in FIGURE 1.

Referring to FIGURE 1, reference numeral 10 defines a cathode tank which rests on rubber wheels 12. A cathode guide plate 14 is mounted horizontally in the cathode tank lit. The cathode guide plate 14 is provided with a plurality of openings 16 and rests on adjustable lugs 18. The number and placement of such adjustable lugs 18 will depend upon the size and design of the cathode guide plate 14. Sutlicient lugs should be provided to adequately support the cathode guide plate 114. Any suit able means can be employed to make the lugs adjustable. One preferred means, as shown in FIGURE 1, comprises a threaded bolt 20 adapted to be inserted into a nut 22 welded or otherwise secured to the bottom of the cathode tank it).

The cathode tank 10 is provided with an electrical connection 24, an outlet 26 for gases generated in cathode tank 16%, and an outlet 28 for the catholyte. The gases generated in cathode tank It) and leaving through outlet 26 can be led into a water box or bubbler (not shown) which would serve as a liquid seal to prevent any air from entering the cell through outlet 26 and creating an explosion hazard in the cell. The catholyte is any liquid in the cathode tank outside of the cathode assemblies 30, hereinafter defined. For example, in the electrolysis of an aqueous solution of sodium chloride, the catholyte after reaction has started, comprises water, some undecomposed sodium chloride, some product sodium hydroxide, and minor amounts of by-products. The outlet 28 can be made adjustable as to height by any suitable means. One such means would be to have the outlet 28 made of threaded pipe in order to allow additional female couplings to be screwed onto the pipe to extend its height.

Referring to FIGURES 1 and 2, numeral 36 defines a cathode assembly which comprises a porous cathode cylinder 32 provided with a flange 34 at the top thereof, a porous bottom portion 36 and a cylindrical foraminous diaphragm 38 which is contiguous with the inner surface of the porous cathode cylinder 32 and the porous bottom portion 36. This foraminous diaphragm 38 is preferably composed of a sleeve portion 37 and a bottom disk 39. A spring 40 is located between the bottom portion 36 of the porous cathode cylinder 32 and the bottom of the cathode tank 10. The porous bottom portion 36 of the porous cathode cylinder 32 is provided with a flange or lip 42. The bottom portion 36 can be an integral or separate portion of the porous cathode cylinder 32, but if the bottom portion 36 is separate, it must be so fitted to the porous cathode cylinder 32 that the catholyte cannot mix with the anolyte. The anolyte will be defined below.

Referring again to FIGURE 1, numeral 44 defines an anode chamber which rests atop the cathode tank 10. A gasket 46 or any other suitable means can be used to seal the anode chamber 44 and the cathode tank 10. The anode chamber 44 is cast with a plurality of depending bosses 43 which rest on the foraminous diaphragms 38 which in turn rest on the flanged portions 34 of the porous cathode cylinders 32. The design of the bottom of the depending bosses 48 and the angle of the flanged portions of the foraminous diaphragms 33 and the porous cathode cylinders 32 are such that, at their point of contact, a seal is formed sufficient to prevent intermixing of the catholyte and the anolyte. The depending bosses 48 are provided with cylindrical openings 50 in their center, through which cylindrical anodes 52 extend from the anode chamber 44 into the cathode assembly 30. The space 54 between the anode 52 and the foraminous diaphragm 38 should be sufficient to allow the free, upward flow of gases formed at the anode without damage to the foraminous diaphragm 33 by the gases so formed. These gases coalesce to form bubbles which ascend upwardly through the anolyte and thence out outlet 58. For example, in the electrolysis of aqueous sodium chloride, chlorine gas forms at the anode 52 and after bubbling up through the anolyte is removed through outlet 58. The anolyte is the liquid present in the anode chamber 44 and the space 54 between the anode 52 and the foraminous diaphragm 38. For example, in the electrolysis of an aqueous solution of sodium chloride, the anolyte after reaction has started, comprises primarily water, sodium chloride, and minor amounts of sodium hydroxide and byproducts, such as hypochlorites.

The space 56 between the top of the catholyte in the cathode tank 19 and the bottom of the anode chamber 44 is termed the cathode gas chamber. The volume of this space 56 varies depending on the height of liquid catholyte maintained in the cathode tank 10. If the cell is operated as an unsubmerged cell, the catholyte level will be very low, yet high enough to form a liquid seal over the outlet 28 in order to prevent any cathode gas from escaping through this outlet 28 or air entering through outlet 28 and causing an explosion hazard in the cell.

Referring to FIGURES l and 3, numeral 66 defines a 4- feed box provided with one or more openings 62 extending partially across the bottom of each of the four sides of the feed box 66 for even distribution of the feed into the anode chamber 44. Suitable means can be employed for keeping the feed box 65 in position, such as a recess in the bottom of the anode chamber 44 to receive and support the lower corners of the feed box 60. The walls of the feed box 66 extend upwardly to the height of the walls of the anode chamber 44. The feed box 60 contains an overflow pipe 66 which extends downwardly through an opening 68 in the bottom of the anode chamber 44 and thence downwardly through first an opening iii in the cathode guide plate 14 and finally through an opening '72 in the bottom or" the cathode tank 10. Suitable sealing means such as rubber gaskets 69 and 73 are provided to prevent leakage around overflow pipe 66 through the opening 68 in the bottom of the anode chamber 44 and the opening 72 in the bottom of the cathode tank 16, respectively. The overflow pipe 66 can be made adjustable by any suitable means. One means, for example, can be to thread the top of the overflow pipe 66 and provide a threaded sleeve pipe 74 which, by being screwed or unscrewed, can regulate the height of overflow pipe 66.

Again referring to FIGURES 1 and 2, the anode 52 is held in a vertical position by a suspension assembly 76 which may or may not be removably attached thereto. The entire suspension assembly 76 and anode 52 can be one solid conductive rod such as a graphite rod, but, preferably, the suspension assembly 76 is removably attached to the anode 52, and, preferably, the upper end of the anode 52 and the lower end of the suspension assembly 76 are threaded to permit a screw fit. While as noted the suspension assembly 76 can be a solid conductive material such as graphite, the interior of the suspension assembly 76 is preferably provided with a hollow central space 78. The hollow central space 78 contains a spring 80. The spring 8 in its relaxed state is longer than the hollow central space 78 so that it presses outwardly against electrically conductive contact disks 82 which are located at either end of the suspension assembly '76. The contact disks 82 are connected to each other by an electrically conductive wire 84. The contact disks 82 are not fixedly attached to the suspension assembly 76. A recess 86 is provided just below the threaded portion at the top of the anode 52 for receiving the contact disk 82 located at the lower end of the suspension assembly 76. It should be noted the spring alone could, if desired, provide the required electrical contact between the anode 52 and the anode top plate underfilling 106 to be described below.

An anode head plate 88 having a central opening 90 coinciding with the inside dimensions of the perimeter of the feed box 6i) rests atop the walls of the anode chamber 44 and the walls of the feed box 6%. Suitable sealing means, for example, a gasket 92 can be employed to seal the anode head plate 88 and the walls of the anode chamber 44. Suitable sealing means, for example, a gasket 94, are provided to prevent leakage between the anode head plate 88 and the walls of the feed box 60. In addition to its central opening 96 exposing the internal portion of feed box 66, the anode head plate 88 has a plurality of other openings 96 from which the suspension assemblies 76 and anodes 52 depend. Suitable sealing means are provided to prevent leakage of gases generated in the anode chamber 44 through these openings 96 in the anode head plate 88. A preferred means comprises a gasket 98 inserted in the recess 100 above the appropriate opening 96 in the anode head plate 88 and fitting into a recess 102 on the exterior of suspension assembly 76 and adjacent the top thereof.

An anode top plate 164 containing an electrically-conductive underfilling 166 rests atop the anode head plate 38. The anode top plate 164 is also constructed with a central opening 168 coinciding with the inside dimensions of the perimeter of the feed box 6% in order to expose the feed box 60 to the atmosphere. The feed box 69 has been shown in FIGURES 1 and 3 as exposed to the atmosphere. The purpose of exposing the feed box 6th to the atmosphere is for ease of feed addition. The central openings 9% and 1% in the anode head plate 38 and the anode top plate 1%, respectievly, can be eliminated, if desired, and other means provided for charging feed to the feed box 69. For example, feed could enter the feed box 6% through an inlet provided in the horizontal plane through the head plate 88 and into feed box 6t). The electrically-conductive underfilling 106 is provided with an electrical connection lit).

The apparatus is assembled in the following manner: The several lugs 13 are adjusted to the desired height and the cathode guide plate 14 is inserted into the cathode tank lit to rest on the adjustable lugs 13. The foraminous diaphragms 33 are placed inside the porous cathode cylinders 32. The springs 40 and the cathode assemblies 369 are inserted through the proper openings 16 in the cathode guide plate 14. The gasket 46 is placed atop the walls of the cathode tank lit. The anode chamber 44 is placed atop the gasket 46. When the anode chamber 44 is placed atop the gasket as, the depending bosses 48 contact the foraminous diaphragms 38 and the flanged tops 34 of the cathode assemblies 359 forming a seal with said foraminous diaphragrns 38 and flanged tops 34 and pushing the cathode assemblies Sti downwardly against the springs 40 and the bottom of the cathode tank 10, thus compressing the springs ll If desired, the springs 44 can be eliminated by providing individual electrical connections to each cathode. If this is done, the cathode guide plate 14 is adjusted upward by lugs 18 so that the flanged tops 34 of the cathode assemblies 36 meet and form a seal with the depending bosses 43 of the anode chamber 44. In this case, it is necessary for the bottoms 36 to be integral with the porous cathode cylinder 32.

The feed box 6 1 is placed into the recess 64 provided for it in the bottom of the anode chamber 44. The overflow pipe '66 is inserted along with its sealing means 69 through the opening as in the center of the recess 64- of anode chamber 44 and thence downwardly through opening 70 in the cathode guide plate 14 and thence downwardly through opening 72 along with sealing means 73 in the bottom of cathode tank 16.

The suspension assembly 76 can be assembled, for example, by inserting the spring 80 into the hollow central space 755, inserting the wire 84 through the helix formed by the spring 8t), and thereafter attaching the ends of the wire 84 to the contact disks 82 by any suitable means such as soldering. The threaded bottoms of the suspension assemblies 76 are screwed into the tops of the anodes 52 thus placing the bottom contact disk 82 into recess 86 provided for it in the top of the anode 52. The anodes 52 are then inserted through the central openings 50 in the depending bosses 48 in the anode chamber 44- and thence into the cathode assemblies 30 so as to stand in an upright position with the bottom of the anodes S2 resting temporarily on the forarninous disks 39 which rest on the bottoms 36 of the porous cathode cylinders 32, until the anodes 52 are raised and suspended inside the cathode cylinders 32 as hereinafter described.

The gasket 92 is placed atop the anode chamber 44 and gasket 94 is placed atop the feed box 69. The openings 96 in the anode head plate 83 are aligned with the contact disks 82 on the tops of the suspension assemblies 76 so that when the anode head plate 38 is placed atop the gaskets 92 and 94, the contact disks 82 on the tops of the suspension assemblies 76 project upwardly through the openings 96 in the anode head plate 88. The contact disks 82 on the tops of the suspension assemblies 76 are lifted upwardly along with the suspension assemblies 76 and the attached anodes 52, and a gasket 98 is inserted around the upper recess 1t52 of each suspension assembly '76. After the gaskets 98 are inserted, the suspension assemblies 76 are positioned downwardly so that the gaskets 98 come to rest in a recess 1% in the anode head plate 83. The combined length of the suspension assembly 76 and the attached anode 52 is such that the bottom of the anode 52 is suspended above the bottom 36 of the cathode assembly 3tl. A certain amount of space between the two is necessary as an accumulation zone for any particles of the anode which may disintegrate and fall to the bottom 36 of the cathode assembly 3%. The height from which the bottom of the anode 52 is suspended above the bottom so of the cathode assembly 30 can vary between about 2 to 4 inches, but is not critical. The anode top plate 1&4 which contains the electrically-conductive underfilling 1% which is bonded or otherwise secured to the anode top plate 164 is placed atop the anode head plate 83 so that its central opening 163 coincides with the central opening 9% in the anode head plate 88. When the anode top plate 194 is placed atop the anode head plate 88, the electrically-conductive underfilling 106 exerts a downward pressure on each of the contact disks 82 on the top of the suspension assemblies 76 compressing springs 86.

The operation of the electrolysis cell as a submerged cathode cell will be described with reference to the electrolysis of an aqueous solution of sodium chloride. The cathode tank id is initially filled with Water to a predetermined level as regulated by the adjustable outlet 28. The water can be added to the cathode tank 10 by any means, for example, water can be added through outlet 28 which would temporarily serve as an inlet. The central opening 76 in guide plate 14 serves as the main passage for the catholyte through the guide plate 14, if the electrolysis cell is operated as a submerged cell.

After the cell is assembled, the aqueous sodium chloride is charged to the feed box 63 through the top central openings 1% and 9t) in the top plate 104 and head plate 83, respectively. The aqueous sodium chloride passes from feed box 63 through the openings 62 at the bottom of the feed box 60 into the bottom of the anode chamber 44 and thence into the space 59 between the inner walls of the depending bosses 43 and the anodes 52 and the space 54 between the cathode assembly (it? and the anode 52. The level of aqueous sodium chloride in the anode chamber 44 is controlled by the height of the overflow pipe 66. This level must be maintained between the top of the openings 62 near the bottom of the feed box 60 and the anode gas outlet 58. The aqueous sodium chloride thus serves as -a liquid seal to prevent any gases generated at the anodes 52 from escaping into the atmosphere via openings 62 and the feed box 61).

There is a pressure exerted on the aqueous sodium chloride between the anode 52 and the cathode assembly 3% by the head of aqueous sodium chloride above it. This pressure helps to prevent the catholyte from entering the space 54 between the cathode 32 and anode 52 by forcing the aqueous sodium chloride through the cathode assembly 39 into the water in cathode tank 10 and thence out outlet 28. The rate of addition of the aqueous salt solution is such as to maintain the desired level in the anode chamber 4 4. The rate at which the aqueous salt solution passes through the cathode assembly 30 depends on the height of liquid in the anode chamber 44 (pressure) and the porosity characteristics of the cathode assembly 30. These porosity characteristics will be discussed hereinafter. After the aqueous sodium chloride is charged to the cell to the desired level, the electrical connections 24 and 110 are made and the genenator is started.

A negative charge is placed on the porous cathode cylinder 32 via the spring 40. the cathode tank It), and electrical connection when the generator is started. Likewise, a positive charge is placed on the anode 52 via the electricaliy-conductive contact disks $2, Wire 84, lead underfiiling 3%, and electrical connection 110 when the generator is started. The anions in the aqueous sodium chloride solution, i.e., the Cl and OH ions, migrate to the anode 52, where the chlorine anions release electrons and form chlorine gas. The chlorine gas coalesces at the anode 52 to form bubbles which proceed upwardly into the top of the anode chamber 44, and thence the chlorine gas, by its own pressure, proceeds out outlet 55. The chlorine gas is prevented from escaping into the atmosphere via the feed box 60 by the liquid seal or" the aqueous sodium chloride solution in the feed box 66 which is maintained at a level above the openings 62 near the bottom of the feed box 65). The hydrogen and sodium cations migrate through the foraminous diaphragm 38 to the porous cathode cylinder 32 where hydrogen gas and sodium hydroxide are formed. The sodium hydroxide dissolves in the water and is eventually removed out outlet 23. The hydrogen gas bubbles upwardly through the catholyte either along the porous cathode cylinder 32 and through openings 16 in guide plate 14 into the cathode gas chamber 56, or through the central opening 70 in the guide plate 14 and thence into the cathode gas chamber 56. The hydrogen gas then passes by its own pressure out outlet 26. This ion migration, followed by the formation of chlorine at the anode 52 and hydrogen and sodium hydroxide at the porous cathode cylinder 32, constitutes the decomposition of the aqueous sodium chloride solution. The catholyte containing water, sodium hydroxide, some undecomposed sodium chloride and minor amounts of by-products is continuously removed during operation through the adjustable outlet 28. The rate of removal of the catholyte through outlet 28 is the function of a number of variables which will be discussed below.

The function of the foraminous diaphragm 38 in the cell is to help reduce the intermixing of the cathodic and anodic products while permitting ions to pass through by electrical migration. For example, in the electrolysis of an aqueous sodium chloride solution, if the sodium hydroxide, a cathodic product, were permitted to mix with chlorine, an anodic product, sodium hypochlorite and chlorates, would form and thus reduce the yield of the desired products, i.e., chlorine and sodium hydroxide. The foraminous diaphragm 38 presents electrical resistance, however, which increases as the diaphragm becomes clogged with impurities which may be present in the aqueous sodium chloride. The rate of flow of aqueous sodium chloride through the foraminous diaphragm 3?: to the porous cathode cylinder 32 and thence to the cathode tank It is a function of the material from which the diaphragm is made, the thickness of the diaphragm, the hydrostatic head under which the aqueous sodium chloride flows, and the resistance offered by the head of fluid in the cathode tank 10. If the aqueous sodium chloride passes too quickly through the foraminous diaphragm 38, the decomposition efiiciency of the cell, which is the ratio of the equivalents of salt decomposed to the equivalents charged, will be impaired. The decomposition efliciency can be increased by reducing the rate of flow of aqueous sodium chloride. This reduction in the rate of flow of the aqueous sodium chloride can be achieved by increasing the density or thickness of the diaphragm, by lowering the level of aqueous sodium cmoride in the anode chamber 44, or by increasing the level of fluid in the cathode tank by means of the adjustable outlet 28. Experimentation in individual cases would be required to determine the proper values for these variables in a cell of the design proposed by the inventor. For example, in one set of experiments in the actual cell employed by the inventor, an asbestos diaphragm was used in the electrolysis of an aqueous sodium chloride solution and the thickness was increased from of an inch to A; of an inch, while holding the other variables constant and the decomposition efficiency was more than doubled.

The material of construction which can be employed ,for the anodes 52 is preferably inexpensive, mechanically strong, as chemically inert as possible, and possessed of good electrical conductivity. Graphite is the preferred material for the anodes and was employed by the inventor for the electrolysis of aqueous solutions of sodium chloride. The graphite can, if desired, be impregnated with substances such as cobalt, linseed oil, synthetic plastics, such as the phenol-formaldehyde, resorcin phenol-formalde hyde, and chemically related products to increase its apparent density and reduce its porosity. Reduced porosity contributes to reduced chemical attack by oxidation. Materials other than graphite which can be used include platinum and gold.

The cathode material is also preferably inexpensive, chemically inert, mechanically strong and electrically conductive. In the refining of metals the cathode is normally made of the metal to be deposited. Iron or steel is the preferred material for fabricating cathodes for diaphragm cells as well as for ot er types of electrolytic cells. Steel cylinders having inch diameter holes spaced A1 inch apart, center to center, were employed by the inventor. The thickness of the cylinder wall was inch. Other suitable materials can be employed. The openings in the porous cathode cylinders 32 are preferably from of an inch in diameter and /s of an inch apart, center to center, to /s of an inch in diameter and A of an inch apart, center to center.

The material from which the cathode tank It} is constructed can be electrically conductive or non-conductive, depending on how the electrical connections to the individual cathodes 32 are made. The cathode tank lid must be electrically conductive, if the electrical connections to the individual cathodes 32 are made through the connection 24, the cathode tank 10, the individual springs 40, and the bottom portions 36 of the cathode assemblies 3 as shown in FTGURES 1 and 2. If this system of electrical connection is employed, a non-conductive coating can be applied to the outside of the cathode tank 16 to prevent accidents to employees through electrical contact, or more preferably, the electrical connection 24 can be made to the bottom of cathode tank 10 which can be made of an electrically conductive material while the sides of the cathode tank 10 can be constructed of a non-conductive material. The cathode tank 10 can be composed entirely of non-conductive material, if individual electrical connections are made to each of the cathode assemblies 30, as described earlier. The material from which the cathode tank lii is constructed must also be physically strong, inexpensive, and chemically inert to attack by substances in the catholyte and products produced at the cathodes 32. The most readily available electrically conductive material which meets these specifications and which was employed by the inventor is steel. Lead could also be employed, particularly if only the bottom of the cathode tank It) is electrically conductive. The electrically non-conductive materials which can be employed include cement, Haveg, Uscolite plastics, hard rubber, or similar materials. Haveg is a manufactured line composed of a mixture of acid digested asbestos and either a phenol-formaldehyde resin or a furane resin.

The material of construction of the anode chamber 44 must be strong, inexpensive, electrically non-conductive and chemically inert to attack by materials in the anolyte and gases produced at the anode 52. For example, in the electrolysis of aqueous sodium chloride, the anode chamber 44 must be chemically inert to attack by chlorine. Cement is the material commonly employed for the construction of anode chambers and was the material employed by the inventor. Materials which can be used include Haveg, Uscolite plastics, hard rubber, etc.

The gaskets 92 and 94 which can be employed to seal the anode head plate 88 from the anode chamber 44 and feed box so, respectively, and gasket 98 employed to seal the electrical conducting under-lining 1% from the gases in the top of the anode chamber 44 must also be composed of material which is chemically inert to attack by gases produced at the anode. For example, in the electrolysis of an aqueous sodium chloride solution, the said gaskets must be chemically inert to attack by chlorine. Such a gasketing material could include, for example, polytetrafluoroethylene (Teilon), asbestos, rubber, and chlorinated rubber. The material employed by the inventor was a mixture of rubber and asbestos.

The material of construction employed in the suspension assembly 76, which suspends the carbon anode 52 from the anode head plate 83 should also, of course, be chemically inert to attack by materials in the anolyte or products produced at the anode 52, for example, chlorine. Teflon would again be a very suitable material, but other less expensive plastics, such as polyethylene, polypropylene, Uscolite plastics, Haveg, etc., or hard rubber, can also be employed, in addition to machinable materials such as graphite. The inventor has employed both graphite and Uscolite plastics.

The material of construction for the top plate 184 must have the same characteristics as the material of construction for the anode chamber 44. Cement was employed by the inventor for the top plate res. The top plate must have an underfilling of an electrically conductive material to carry the charge from the generator to the conductors in the various suspension rods and thence to the individual anodes. The conductive underfilling of the top plate is usually lead, since it is cheap and has good conductivity. Other conductive materials which can also be employed include copper, silver and aluminum.

As noted above, the purpose of the formainous diaphragm 38 in the cell is to serve as a barrier and thus help reduce the int rmixture of fluids in the anode and cathode chambers while, at the same time, remaining porous enough to permit ion migration to and from the porous cylinder 32 which serves as a cathode. The preferred material, and the one used by the inventor, for the foraminous diaphragm 33 is asbestos, since it is lightweight, sturdy and possesses the proper porosity.

The rate of flow of feed into the feedbox sewill be approximately equal to the rate of removal of the catholyte through outlet be a function of the size of the cell, the electrical efficiency of the cell, and the concentration of the salt solutions. There will, of course, be adjustments in these rates when it is desired to change the liquid levels in the anode and cathode chambers. For example, in the electrolysis of a saturated solution of sodium chloride in a ce l of the design proposed by the inventor, which contained 762 square inches of anode area, the rate of flow of brine to the unit varied from about 0.5 to about 4.5 gallons per hour.

in the electrolysis of aqueous solutions of salts, the concentration of salt is not critical. It is preferred that the solutions be as concentrated as possible without precipitation of salt in the cell. Saturated salt solutions at the operating temperature of the cell are thus preferred.

The operating temperature of the cell is not critical. An increased temperature will decrease the solubility of chlorine in the anolyte, but will correspondingly increase the rate of undesired side reactions such as the formation of sodium hypochlorite and chlorates which will attack and destroy the anodes. The operating temperature of the cell can be, for example, from 110 to 150 F., with preferred operating temperatures between 125 F. to 145 F.

The electrolysis of an aqueous solution of sodium chloride will be used as a specific example of the operation of the cell of this invention. The experimental cell was of the design shown in FIGURES 1 to 3 of this application. The porous cathode cylinders 32 were 3.5 inches in diameter and inches long, and the foraminous diaphragms 38 consisted of two thicknesses of inch sheet asbestos. The anodes 52, consisted of carbon cylinders 2.5 inches in diameter and 12 inches long. The eight anodes contained a total of 762 square inches of area. The distance, exclusive of the diaphragm, between the The rate of feed addition will walls of the porous cathode cylinder 32 and the anodes 52, was approximately 0.5 inch. The cathode tank 10 was 18 inches square and 12 inches high. The anode chamber 44 was 18 inches square and 15 inches high with a reinforced concrete top. The feed box 6t? was 5 inches square and 6 inches high. An aqueous solution of sodium chloride (brine) having an analysis as shown in Table 1 below was charged to the cell at an average rate of 1.36 gallons per hour.

TABLE I Analysis of Brine t0 the Cell Analysis:

Specific gravity, 60/60 -F 1.204 Chlorides, as NaCl, percent by wt 25.3 Sodium hypochlorite, percent by wt Nil Calcium, parts per million Nil Magnesium, parts per million Nil *Iron, parts per million Nil The cell was operated at atmospheric pressure and F. The voltage drop across the cell was 3.9 volts. The current density, i.e., the amperes per square inch of anode was 0.26. The cell eflluent, i.e., the catholyte, contained 026 gram of sodium chloride per milliliter. The cell produced in one day 13.8 pounds of chlorine, 0.39 pound of hydrogen, and 15.9 pounds of sodium hydroxide. The voltage, current and energy efficiencies were 59.2, 98.5 and 58.3 percent, respectively. These efficiencies were calculated by the method proposed by Norris R. Shreve in his book entitled The Chemical Process Industries, first edition, page 285, McGraw-l-lill Book Company, Inc, New York, 1945.

Obviously many modifications and variations of the invention as hereinabove set forth can be made without departing from the spirit and scope thereof, and therefore only such limitations should be imposed as are indicated in the appended claims.

I claim:

1. An electrolytic cell comprising a cathode tank, a cathode assembly comprising a permeable cathode electrode and a foraminous diaphragm contiguous with the inner surface of said permeable cathode electrode, means for suspending said cathode assembly in said cathode tank in a veutical position, means for making electrical contact with said permeable cathode electrode; an anode chamber atop said cathode tank, said anode chamber containing a depending boss resting on the top of said pereable cathode electrode; a solid anode suspended in a vertical position inside said cathode assembly and extending upwardly into said anode chamber through a cen tral opening in said depending boss of said anode chamher; a suspension assembly for holding the anode in a verical position, said suspension assembly being removably attached to said anode, and said suspension assembly comprising a hollow suspension rod, an electrically-conductive spring positioned inside said hollow suspension rod, electrically-conductive contact disks positioned at either end of said suspension rod, and an electricallyconductive wire positioned through the helix of said electrically-conductive spring in said hollow of said suspension rod with said electrically-conductive wire attached to said electrically-conductive contact disks on either end of said suspension rod; means for keeping the suspension assembly in suspension and means for making an elec trical connections with said electrically-conductive contact disks.

2. An electrolytic cell comprising a cathode tank, a cathode assembly comprising a permeable cathode electrode and a foraminous diaphragm contiguous with the inner surface of said permeable cathode electrode, means for suspending said cathode assembly in said cathode tank in a vertical position, an electrically-conductive spring inserted between the bottom of said cathode assembly and the bottom of said cathode tank; means for making eleclit trical connection with said electrically-conductive spring; an anode chamber atop said cathode tank, said anode chamber having a depending boss resting on the top of said permeable cathode electrode; a solid anode suspended in a vertical position inside said cathode assembly and extending upwardly into said anode chamber through a central opening in said depending boss of said anode chamber; means for suspending said anode in a vertical position which means are electrically conductive; and means for making an electrical connection with said electrically conductive suspension means.

3. An electrolytic cell comprising a cathode tank, a cathode assembly comprising a permeable cathode electrode and a foraminous diaphragm contiguous with the inner surface [of said permeable cathode electrode, means for suspending said cathode assembly in said cathode tank in a vertical position, an electrically-conductive spring inserted between the bottom of said cathode assembly and the bottom of said cathode tank; means for making electrical connection with said electrically-conductive spring; an anode chamber atop said cathode tank, said anode chamber having a depending boss resting on the top of said permeable cathode electrode; a solid anode suspended in a vertical position inside said cathode assembly and extending upwardly into said anode chamber through a central opening in said depending boss of said anode chamher; a suspension assembly for holding the anode in a vertical position, said suspension assembly being removably attached to said anode, and said suspension assembly comprising a hollow suspension rod, an electrically-conductive spring positioned inside said hollow suspension rod, electrically-conductive contact disks positioned at either end of said suspension rod, and an electrically-conductive Wire positioned through the helix of said electrically-conductive spring in said hollow of said suspension rod with said electrically-conductive wire attached to said electrically-conductive contact disks on either end of said suspension rod; means for keeping the suspension assembly in suspension and means for making an electrical connection with said electrically-conductive contact disks.

4. An electrolytic cell comprising a cathode tank, a plurality of cylindrical cathode assemblies comprising a plurality of cylindrical permeable cathode electrodes and a plurality of toraminous diaphragms contiguous with the inner surfaces of said cylindrical permeable cathode electrodes, means for keeping said cathode assemblies in place in said cathode tank, a like plurality of electricallyconductive springs inserted between the bottom of said cylindrical cathode assemblies and the bottom of said cathode tank, an anode chamber atop said cathode tank, said anode chamber having a plurality of depending bosses resting and coinciding with the tops of said cylindrical permeable cathode electrodes, a plurality of cylindrical solid anodes suspended in a vertical position inside said cylindrical cathode assemblies and extending upwardly into said anode chamber through central openings in said depending bosses of said anode chamber, an anode head plate resting atop the anode chamber said anode head plate containing a plurality of openings, a plurality of suspension assemblies for holding said anodes in said vertical position, said suspension assemblies being removably attached to said anodes and said suspension assemblies comprising a hollow suspension rod, an electricallyconductive spring positioned inside said hollow suspension rod, electrically-conductive contact disks positioned at either end of said suspension rod and an electricallyconducti-ve =Wire positioned through the helix of said electrically-conductive spring in said hollow of said suspension rod with said electrically-conductive wire attached to the electrically-conductive contact disks on either end of said suspension rod; means for securing the suspension assemblies in the plurality of openings provided in said anode head plate, means for securing electrical connection between said electrically-conductive springs and said cathodes and between said electrically-conductive disks and said anodes, means for introducing said feed into the anode chamber of said cell and means for removing products produced in the cell.v

5. An electrolytic cell comprising a cathode tank, a guide plate mounted on a horizontal plane in the cathode tank, said guide plate provided with a plurality of openings; a plurality of cathode assemblies inserted into the plurality of openings in said guide plate, each of said cathode asse blies comprising a permeable cathode electrode and a foraminous diaphragm contiguous with the inner surface of said permeable cathode electrode, a like plurality of electrically-conductive springs inserted between the bottom of said cathode assembly and the bottom of said cathode tank, means for making an electrical connection through said cathode tank to said electricallyconductive springs, an anode chamber atop said cathode tank, said anode chamber containing a plurality of de pending bosses resting and coinciding with the tops of said cathode assemblies, a plurality of solid anodes suspended in a vertical position inside said cathode assemblies and extending upwardly into said anode chamber through central openings in said depending bosses of said anode chamber, an anode head plate resting. atop said anode chamber, said anode head plate having a plurality of openings, a plurality of suspension assemblies for holding said anodes in said vertical position, said suspension assemblies being removably attached to said anodes and each of said suspension assemblies comprising a hollow suspension rod, an electrically-conductive spring positioned inside said hollow suspension rod, electricallyconductive contact :disks positioned at either end of said suspension rod and an electrically-conductive wire positioned through the helix of said electrically-conductive spring in said hollow of said suspension rod with said electrically-conductive Wire attached to the electricallyconductive contact disks on either end of said suspension rod; means for securing the suspension assemblies in the plurality of openings provided in said anode head plate, an anode top plate resting atop the anode head plate, said anode top plate containing an electrically-conductive undeifilling, a feed box in said anode chamber provided with openings to allow the feed to flow into said anode chamber, means for controlling the height of (feed in the feed box and means for removing products produced in the cell.

References Qited in the file of this patent UNITED STATES PATENTS 1,373,394 Allen Apr. 5, 1921 1,404,387 Green Jan. 24, 1922 1,477,629 Chrisman Dec. 18, 1923 1,798,575 Allen et a1 Mar. 31, 1931 

1. AN ELECTROLYTIC CELLCOMPRISING A CATHODE TANK, A CATHODE ASSEMBLY COMPRISING A PERMEABLE CATHODE ELECTRODE AND A FORAMINOUS DIAPHRAGM CONTIGUOUS WITH THE INNER SURFACE OF SAID PERMEABLE CATHODE ELECTRODE, MEANS FOR SUSPENDING SAID CATHOD ASSEMBLY IN SAID CATHODE TANK IN A VERTICAL POSITION, MEANS FOR MAKING ELECTRICAL CONTACT WITH SAID PERMEABLE CATHODE ELECTRODE; AN AMODE CHAMBER ATOP SAID CATHODE TANK, SAID ANODE CHAMBER CONTAINING A DEPENDING BOSS RESTING ON TOP OF SAID PERMEABLE CATHODE ELECTRODE; A SOLID ANODE SUSPENDED IN A VERTICAL POSITION INSIDE SAID CATHODE ASSEMBLY AND EXTENDING UPWARDLY INTO SAID ANODE CHAMBER THROUGH A CENTRAL OPENING IN SAID DEPENDING BOSS OF SAID ANODE CHAMBER; A SUSPENSION ASSEMBLY FOR HOLDING THE ANODE IN A VERTICAL POSITION, SAID SUSPENSION ASSEMBLY BEING REMOVABLY ATTACHED TO SAID ANODE, AND SAID SUSPENSION ASSEMBLY 